Marcasite at the Permian‐Triassic Transition

Thomas J Algeo,Leonid Danyushevsky,Ross R Large,Daniel Mantle,Jeffrey A Steadman,Thomas Rodemann,Kliti Grice,Elena Lounejeva

doi:10.1002/9781119507444.ch16

Thomas J Algeo, Leonid Danyushevsky + Show 6 more

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https://doi.org/10.1002/9781119507444.ch16

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Abstract

Abundant pyrite in black shales at the Permian-Triassic Boundary (PTB) from several localities around the world has been regarded as evidence of oceanic anoxia during the end-Permian mass extinction (EPME). However, a significant amount of the “pyrite” in these rocks is not actually pyrite but marcasite, the orthorhombic polymorph of FeS2. Marcasite is particularly sensitive to changes in pH and fO2, which theoretically enables it to be utilized as a proxy for geochemical changes in the marine environment. Moreover, its abundance in these PTB rocks suggests that major geochemical changes occurred at this time in the global ocean. In this chapter, we present stable isotope and trace element compositional data for both marcasite and pyrite, which were identified in the stratigraphic interval representing the EPME, along with bulk-rock chemostratigraphic data for the Kockatea Shale, Perth Basin, Australia. We compare marcasite-pyrite intergrowth textures in PTB sedimentary sequences from Meishan D (MD), Opal Creek (OC), Ubara (Ub), and the Kockatea Shale (KS), which represent both shallow continental shelves of the ancient Tethys Ocean (KS, MD) and the abyssal plains of the Panthalassic Ocean (Ub, OC) at the end of the Permian. The textures, trace element geochemistry, and sulphur isotopic analyses of these samples favor a synsedimentary to early diagenetic origin for the sulfides, further supporting the notion that the EPME was at least partially caused by a large-scale pH drop in the global ocean at the PTB. A review of other sedimentary sequences around the globe, including pre- and post-Permian sections, indicates that sedimentary-diagenetic marcasite may be more abundant in the rock record than previously recognized, which carries implications for the geochemistry of the marine environment through geologic time.

Highlights

Ocean anoxia and hydrosphere acidification are likely consequences of a massive release of volatiles in a complex cause‐ and‐effect relationship between the Siberian Traps large378 LARGE IGNEOUS PROVINCESRedox analysis in ancient marine sediments commonly makes use of shales and the pyrite present in them
Acid rain at the end‐Permian has been linked to a massive release of volatiles (S, Cl, F) from the Siberian platform sediments during the STLIP formation, and this process may have been an important cause of the contemporaneous terrestrial ecosystem failure and ozone‐layer collapse (Black et al, 2013), the effect of acidification on the extinction of heavily calcifying marine organisms is poorly understood (Doney et al, 2009; Hofmann et al, 2010; Veron, 2008)
We review the existing literature on marcasite formation through different geological processes and bring together disparate records about marcasite occurrences at the end‐Permian and other younger and older stratigraphic boundaries associated with mass extinctions

Summary

Introduction

Ocean anoxia and hydrosphere acidification (i.e., acid rain and/or ocean acidification) are likely consequences of a massive release of volatiles in a complex cause‐ and‐effect relationship between the Siberian Traps large378 LARGE IGNEOUS PROVINCESRedox analysis in ancient marine sediments commonly makes use of shales and the pyrite present in them. The presence of gypsum in white clay layers lacking carbonates immediately preceding the major mass extinction event in the middle of the Bed was proposed as mineralogical evidence of the end‐Permian marine acidification by hydrated sulphuric acid, leading to a pH drop below 3.89 (Liang, 2002). This hypothesis has been widely cited but has not received further support, stable isotopes of coexisting pyrite and gypsum from cold seeps have provided evidence of variable methane emissions (Lin et al, 2016). Hot acidic Late Permian seas were proposed based on extraordinarily high 187Re/188Os ratios and high contents of Re accumulated in P‐T successions from the mid‐Norwegian shelf and East Greenland (Georgiev et al, 2015)

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